tips for camping in fog ... or not camping in the fog

Introduction

fog occurs either when:
- the air temperature drops below its dewpoint
  - ground inversion when the ground cools overnight especially on clear nights with no wind, cooling the air nearest the ground
  - wind pushing moist air to rise up a mountain slope results in adiabatic cooling to its dew point forming upslope fog which generally forms at higher elevations and builds downwards into valleys
  - advection inversions
    - cold air flowing from higher ground to pass under lower warmer air in valleys
    - warm air flowing over a cold ocean which cools the lower layers of the wind
- the air dewpoint rises above the air temperature
  - fog over relatively warm rivers and lakes in autumn and early winter which create increased humidity in colder air above it
obviously if camping at higher altitudes you may experience “fog” when clouds at your altitude close in
as the mass and the specific heat of water is much higher than air, it takes a lot more heat to raise the temperature of moist air or fog than dry air

this is generally an unpleasant experience as the fog permeates through into almost everything that that is not airtight and waterproof - ie. it gets inside your tent and can make you, your sleeping gear and clothes wet and even create puddles of water inside your tent
you thus end up wet and cold unless you have some form of heating inside your tent to increase the tent air temperature above its dewpoint and stop it forming dew droplets
- see hot tents (tents with wood stoves inside)

especially if it is a clear cold night with no wind, with air having a relatively high dewpoint, fog risk is high, seek higher ground away from water bodies (ie. avoid bottoms of valleys) and low lying areas of ground with perhaps a little more of a breeze
if you are in the mountains, try to camp below the cloud line and above the valley cloud line
the more moist the ground, the higher the chance of fog
- avoid camping over grassy areas which have higher moisture contents and more likely to form dew or fog
- a rapidly clearing sky after rain increases the risk of fog, especially if there is little wind
you are much less likely to have fog on the downslope of a mountain than an upslope in terms of wind direction
morning sun will tend to dissipate fog rapidly by warming the ground and it will help to dry out your tent/tarps/etc.

reduce ground fog/dew by placing a tarp over the ground to reduce heat radiation from the ground
raise the air temperature above its dewpoint
- create a microclimate to retain your body heat - tarps/blankets outside the tent
- increase heating inside your tent eg. heated water bottle
ensure you have adequate ventilation to address condensation issues from your expired breaths
place your clothes in airtight waterproof bags
have a towel to mop up condensation
ensure the rain fly has a steep slope to allow any fog condensation on its under-surface to run off instead of fall into your tent
use a well ventilated fabric inner tent so that any fog condensation on the under-surface of the fly dropping onto your inner canopy runs off rather than through mesh